Patent Document 1 discloses a conventional scroll compressor. This scroll compressor includes a housing, a fixed scroll fixed inside the housing and forming a discharge chamber between the fixed scroll and the housing, a movable scroll supported inside the housing such as to orbit only around an orbit axis and forming compression chamber chambers between the movable scroll and the fixed scroll, and a shaft support member fixed inside the housing and forming a back pressure chamber between the shaft support member and the movable scroll.
The fixed scroll includes a fixed base plate and a fixed spiral wrap integral with the fixed base plate. The movable scroll includes a movable base plate facing to the fixed base plate, and a movable spiral wrap integral with the movable base plate and meshing with the fixed spiral wrap. When the movable scroll orbits, the compression chambers defined by the fixed base plate, the fixed spiral wrap, the movable base plate, and the movable spiral wrap move toward the center with a progressively decreasing volume, as a result of which the refrigerant gas inside the compression chambers are compressed. A cylindrical spinning boss is formed on the side of the movable scroll facing the back pressure chamber.
The movable base plate of the movable scroll is formed with a narrow hole for supplying the refrigerant gas inside the compression chambers into the back pressure chamber as the chambers move toward the center. The outer periphery of the movable base plate that is in sliding contact with the outer periphery of the fixed base plate is concavely formed an annular groove. The annular groove communicates with the inside of the spinning boss through a communication hole formed inside the movable scroll.
Between the housing and the shaft support member is formed a motor chamber accommodating an electric motor for driving the movable scroll. The rotating shaft of the electric motor is rotatably supported by the housing and the shaft support member. The discharge chamber and the motor chamber communicate with each other through a through hole formed on an outer circumferential side of the fixed scroll and the shaft support member.
An eccentric portion convexly formed at one end of the rotating shaft of the electric motor rotatably fits in the spinning boss. The rotating shaft is formed with an oil supply hole that communicates the motor chamber with the inside of the spinning boss.
In this scroll compressor, as the movable scroll is driven by the electric motor and orbits, the refrigerant gas is compressed in the compression chamber to a high pressure and discharged to the outside through the discharge chamber and the motor chamber.
Now, in this scroll compressor, during low-load operation, the refrigerant gas at an intermediate pressure inside the compression chamber is supplied to the back pressure chamber through the narrow hole of the movable base plate so as to bias the movable scroll toward the fixed scroll to a suitable extent. In this case, the outer peripheries of the fixed base plate and the movable base plate are in sliding contact with each other, with lubricating oil contained in the refrigerant gas being present therebetween. Oil film of this lubricating oil acts as an oil seal, providing a seal between the annular groove and the back pressure chamber. Therefore a power loss hardly occurs in the orbital motion of the movable scroll, and a refrigerant gas leak is unlikely to occur.
On the other hand, during high-load operation, the movable scroll cannot be biased sufficiently toward the fixed scroll by merely supplying the refrigerant gas at an intermediate pressure in the compression chamber to the back pressure chamber through the narrow hole. In this case, the movable scroll is subjected to a force that causes it to tilt relative to the fixed scroll, i.e., an overturning force. Because of this, the outer peripheries of the fixed base plate and the movable base plate separate from each other, breaking the oil seal that was sealing the annular groove. The annular groove and the back pressure chamber thereby communicate with each other, allowing the refrigerant gas at a discharge pressure inside the motor chamber to be supplied to the back pressure chamber via the oil supply hole, inside of the spinning boss, the communication hole, and the annular groove, so as to raise the pressure inside the back pressure chamber. This scroll compressor is capable of biasing the movable scroll toward the fixed scroll to a suitable extent in this manner even during high-load operation.